| Scenario | Tank capacity | Levels | Flow | Efficiency | Estimated time |
|---|---|---|---|---|---|
| Rain barrel top-up | 200 L | 25% → 90% | 12 L/min | 0.90 | ~12 min |
| Drip tank refill | 55 US gal | 40% → 95% | 6 US gal/min | 0.85 | ~10 min |
| Rectangular trough | 100×60×50 cm | 10% → 80% | 10 L/min | 0.80 | ~17 min |
| Bucket-tested faucet | 300 L | 0% → 75% | 10 L in 55 sec | 0.90 | ~21 min |
- Tank volume (direct): capacity in your chosen unit, converted to liters.
- Rectangular volume: V = L × W × H, then convert m³ to liters.
- Cylindrical volume: V = π × r² × H, then convert m³ to liters.
- Water needed: Needed = TankVolume × (Target% − Current%) / 100
- Effective flow: EffectiveFlow = FlowRate × Efficiency
- Base time: BaseMinutes = Needed / EffectiveFlow
- Total time: TotalMinutes = BaseMinutes + BufferMinutes + (PauseSeconds × Pauses)/60
- Pick the tank method: direct capacity, rectangular, or cylindrical.
- Enter current and target levels: use the same level scale.
- Choose a flow method: direct rate or bucket test.
- Set efficiency: reduce for long hoses, filters, or low pressure.
- Add a buffer: useful for float valves and sensor delays.
- Calculate: read results above the form after submission.
- Download reports: export CSV for logs, PDF for sharing.
Sizing the reservoir for irrigation cycles
Work from usable volume, not the label capacity. A 200 L barrel filled from 25% to 90% adds 130 L. If beds need 40 L daily, that refill covers about three days. For frequent top‑ups, use smaller percentage swings to reduce float valve chatter and sediment disturbance. The calculator converts rectangular and cylindrical dimensions to liters for consistent comparisons. This reduces surprises when multiple zones refill the same reservoir overnight.
Measuring real flow at the source
Tap and pump ratings can be optimistic. The bucket test gives an on‑site number: 10 L in 55 seconds equals about 10.9 L/min. Repeat twice and average to reduce timing error. Logged tests also reveal seasonal pressure drops and clogged filters. Switch units to match your tools, then export CSV results for maintenance notes.
Accounting for losses and restrictions
Effective flow is rarely the same as stated flow. Long hoses, elevation, screens, and backflow devices reduce delivery. Use efficiency as a practical factor: 0.90 for short runs, 0.75 for long hose plus filter, and 0.60 for marginal pressure. Example: 12 L/min at 0.80 becomes 9.6 L/min, pushing a 150 L refill from 12.5 to 15.6 minutes.
Adding buffers for control hardware
Float valves and solenoids do not stop instantly. Add a buffer in minutes for sensor delay, pressure spikes, or small leaks. If the valve cycles, include pause seconds and expected pauses to reflect stop‑start behavior. A 5‑second pause repeated 30 times adds 2.5 minutes, which matters for timed irrigation. Total time combines base minutes, buffer minutes, and cycling pauses.
Planning run windows and overflow protection
Enter a start time to estimate a finish time, useful for off‑peak pumping or quiet hours. Pair the estimate with overflow protection: a high‑level shutoff, an air gap, or a secondary drain path. For fertigation, finish time helps coordinate mixing and injection. Review warnings for zero flow or equal levels, then share a PDF report with helpers and prevents accidental overflow events.
What efficiency value should I use?
Use 0.90 for short hose runs, 0.75 for long hose plus filter, and 0.60 for low pressure or many fittings. If results feel optimistic, lower efficiency until your estimates match real refills.
How do I do a bucket test correctly?
Use a known container size, start timing when flow stabilizes, and stop at the fill mark. Repeat two or three times and average. Enter bucket volume and seconds to get an on‑site flow rate.
Why is my time longer than expected?
Common causes are pressure drops, clogged screens, hose kinks, elevation gain, or a low efficiency setting. Also check that target percent is above current percent and that the tank volume method matches your container.
Can I estimate finish time for an overnight refill?
Yes. Enter a start time and the tool estimates a finish time based on total seconds. If you expect valve cycling or pump pauses overnight, add pause seconds and an estimated number of pauses for a safer schedule.
What should I enter for “cycles” and “pause seconds”?
Use them when a valve or pump repeatedly stops and restarts. Count typical stop‑start events during a fill, estimate the average pause length, and enter both. The calculator converts that downtime into added minutes.
Is it better to fill from 0% to 100%?
Not always. Large swings can stir sediment and increase overflow risk if sensors lag. Many gardens refill between two marks, like 25% to 90%, and add a small buffer. Pair with a shutoff for safety.